A molybdate (Ⅵ)-Al(Ⅲ) chemical conversion process was developed as an alternative to the chromate processes. Steel and zinc-plated steel specimens were treated in the solutions of 0.16 moll~-1 ammonium alum (AlNH_4(SO_4)_2.12H_2O) with small amounts of ammonium molybdate (Ⅵ) (0.002-0.016 moll~-1 (NH_4)_6Mo_7O_24.4H_2O) at 60 deg. C for 10-30 min in an ul- transonic rinsing apparatus. The formed films were composed of oxyhydroxides containing Mo(Ⅴ,Ⅵ), Al(Ⅲ), Fe(Ⅱ,Ⅲ), and sulfate ions (and Zn(Ⅱ) ions in the case of zinc-plated steel), And showed good corrosion resistance in an aerated 0.5 moll~-1 NaCl-0.15 moll~-1 H_3BO_3 Solutin (pH=7).
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